Over the past year, the world's worst ever outbreak of Ebola, a highly infectious haemorrhagic fever, has killed over 7,900 people, with more than 20,000 cases recorded mostly in Guinea, Sierra Leone and Liberia. The virus is still spreading in West Africa, especially in Sierra Leone.
A week ago, 39-year-old Pauline Cafferkey, who had been working in West Africa with the charity Save the Children, became the first person to be diagnosed with the disease in Britain.
She had flown from Sierra Leone to Scotland via Morocco and London and was screened for a high temperature with other returning health workers at Heathrow but showed no signs of fever. When she requested further screening, six subsequent checks were within normal levels and she continued her journey.
Britain began screening passengers from West Africa for symptoms of Ebola in October.
"We have ... strengthened our guidance to ensure that anyone from a high-risk group who feels unwell will be reassessed, advice will be immediately sought from an infectious diseases specialist and the passenger will be referred for testing if appropriate," Health Secretary Jeremy Hunt told parliament, saying the new procedures had been in place since December 29.
"Even if someone isn't displaying symptoms but says they are feeling a bit under the weather, then we would isolate them if they are in the high-risk category," Hunt said.
On Saturday the hospital treating Cafferkey said she had deteriorated and was now in a critical condition. Hunt said that while she remained critical, her condition had stabilized.